1. Field of the Invention
This invention relates to a method for reducing the size of a digital file and for reading the file thus reduced. It is more particularly applicable to digital image or video files for which the digital data are compressed or not compressed or that may have to be compressed after reduction.
It is particularly aimed at reducing the scale of digital values transmitted to the encoder, for example up to ⅕° of the original scale represented by its 51 lowest brightness values.
In the case of decoding, these 51 reduced brightness values are reproduced on a larger scale in which the values are separated into sets of 5 and are calibrated from 3 to 253, only inducing an average error of 1% from the original data.
2. Description of the Prior Art
Conventionally, digital data are translated by numbers encoded on a scale from 0 to 255. In the context of a fixed length binary coding, the highest number being used as a reference, each character is coded on eight bits. In the context of a variable length binary coding, the allocation of bits refers to the probability of occurrence of each character, without taking account of the height of the characters. However, the efficiency of this coding depends on the number of values to be coded and the total length of the character string to be compressed.
To overcome this problem and thus reduce the number of bits used, existing compression systems record variations that characterize the pitch separating two or more values. Although this option tends to reduce their height, it often extends their range and does not provide a perfect answer to the problem because variations depend on the maximum difference between the original digital values of which they are only the translation.
More generally, a greater reduction in the size of a digital audio and video file traditionally makes it necessary to respect four constraints, the first and last of which are antinomic:                reduce the number of values to be encoded,        reduce the extent of their range,        reduce the length of the character string,        keep as much information as possible to guarantee a reproduction as similar as possible to the original.        